The present invention is related to integrated circuits. More specifically, the present invention can be applied to controllers used for switch mode power supply. According to various embodiments, the present invention provides integrated power switch implemented with different types of transistors. Merely by way of example, the present invention can be used in switch mode power conversion system including, among other things, offline fly-back converters and forward converters. But it would be recognized that the invention has a much broader range of applicability.
Power converters are widely used in various applications, such providing power to portable consumer electronics. The power converters can convert electric power from one form to another form. As an example, the electric power is transformed from alternate current (AC) to direct current (DC), from DC to AC, from AC to AC, or from DC to DC. Additionally, the power converters can convert electric power from one voltage level to another voltage level.
In the past various types of power converters have been developed. For example, linear regulators have traditionally been used for power converters. A linear regulator is a voltage regulator based on an active device (such as a bipolar junction transistor, field effect transistor or vacuum tube) operating in its “linear region” or passive devices like zener diodes operated in their breakdown region. The regulating device is made to act like a variable resistor. While linear regulators have been used for many years, their power efficiency is often inadequate for portable electronics. For example, due to low power efficiency, linear regulators often waste large amount of energy and generate excessive heat for portable devices.
With the advent of integrated circuits, switched-mode power supply has been invented and utilized for various applications. Switch mode power supplies are typically implemented with a switching regulator, which is an internal control circuit that switches the load current rapidly on and off in order to stabilize the output voltage. For certain applications, switch mode power supply uses pulse-width-modulated (PWM) or pulse-frequency-modulated (PFM) mechanism. These mechanisms are usually implemented with a switch-mode-controller including various protection components.
In a switching power conversion system, various types of transistors are used to implement power switching elements. For example, power MOSFET, power bipolar transistor (BJT), Insulated Gate Bipolar Transistor (IGBT), or other types transistors have been used. Usually, the power switching elements are controlled by PWM, PFM or other types of control signal are adjusted based on feedback from output. For example, fly-back configuration is used to enable the feedback system. The output voltage and/or current is regulated by sensing the output voltage or current and applying the corresponding control signals to the power switching elements.
FIG. 1 is a simplified conventional switch mode converter implemented with PWM feedback configuration. This diagram is merely an example, which should not unduly limit the scope of the claims. One of ordinary skill in the art would recognize many variations, alternatives, and modifications. A switch mode converter 100 includes an OCP comparator 110, a PWM controller component 120, a gate driver 130, a power switch 140, resistors 150, 152, 154, and 156, and a primary winding 160. For example, the OCP comparator 110, the PWM controller component 120, and the gate driver 130 are parts of a chip 180 for PWM control. When the current of the primary winding is greater than a limiting level, the PWM controller component 120 turns off the power switch 140 and shuts down the switch mode power converter 100.
During operation, the PWM controller component 120 is used to control and drive a power switch 140, which turns on and off to control the power delivered to the load in the secondary side. For example, the power switch 140 is a power MOSFET. In general, separate PWM controller module and the power MOSFET are widely used.
As mentioned above, switch regulators such as the conventional switch mode converter illustrated in FIG. 1 has various advantages over linear regulators. However, for various applications, the conventional switch mode converter is often inadequate. For example, switching regulators are typically more complex and more expensive, their switching currents can cause noise problems if not carefully suppressed, and simple designs may have a poor power factor.
Therefore, it is desirable to have an improved system and method for switching power conversion system.